Portable tire sealing and inflating aerosols are well known. These specialty items were introduced during the early 1960's and currently represent a market of about 30,000,000 units per year in the U.S.A. alone. Carrying a product of this type assures motorists that they can make fast repairs when confronted with a flat or under-inflated tire. This can be important if the driver happens to be in a remote, inclement or dangerous location, or if the vehicle does not contain a suitably inflated spare tire.
A significant number of prior art tire sealant and inflator compositions have been described in the patent literature since 1968. Typically, this literature discloses various water-based or sometimes anhydrous formulations, comprising a polymeric sealant, an anti-freeze ingredient, an emulsifier, aerosol can corrosion inhibitors, and occasionally the use of solids, such as asbestos fibers, fiberglass fibers, or (simply) fibers. The cited U.S. Patents by Kent, Ornum and Magyar are typical. All patents cited as references are incorporated herein as if reproduced in full below.
The described composition must also include a propellant designed to quickly evacuate the self-pressurized contents of the dispenser into the tire via a short length of connecting hose that is supplied with the product. The ideal propellant will have a substantial vapor pressure in the aerosol can, even at low temperatures, and be capable of generating sufficient pressure in tires so that the vehicle can be safely driven. The ideal propellant will also be non-inflammable, non-toxic, non-corrosive and reasonably inexpensive.
During the past decade, such non-flammable propellants as dichlorodifluoromethane (CCI.sub.2 F.sub.2), sym.dichlorotetrafluoroethane (CCIF.sub.2 --CCIF.sub.2), with CCI.sub.2 F.sub.2, and monochlorodifluoromethane (CHCIF.sub.2) have been used commercially for tire sealant/inflator products. However, each of them has been noted as evidencing significant (stratospheric) ozone depletion potential, and their use has now been severely limited to only the most essential type aerosol products.
More recently, U.S. Pat. No. 5,124,395 to Abramowski disclosed the use of 1,1,1,2-tetrafluroroethane (CH.sub.2 F--CF.sub.3) as a non-flammable propellant. While not having stratospheric ozone depletion potential (ODP), this very stable gas has a very significant global warming potential (GWP), sometimes called a green-house effect. It is 2,250 times as potent as carbon dioxide as a global warming agent and, because of this, major suppliers are severely restricting its use to those aerosol products considered essential for life-saving or military applications.
At this time, no other commercially available non-flammable propellant liquids are available which do not evidence significant environmental short-comings. Some laboratory curiosities exist, such as perfluorodimethyl ether (CF.sub.3 --O--CF.sub.3), but the economics of toxicological testing, plant construction and verification of environmental compatibility status make their commercialization very unlikely. Because of this, the three-component blend described in the present invention appears to be an optimum choice between the non-flammable (but unavailable) propellants, and the extremely flammable (generally used) propellants for tire sealing and inflating aerosols.
The so-called high pressure compressed gases, such as carbon dioxide (CO.sub.2), nitrous oxide (N.sub.2 O), nitrogen (N.sub.2) and air (N.sub.2 /O.sub.2), are both environmentally acceptable and non-flammable, but, by themselves, are totally ineffective as tire inflators. This is because relatively little of these gaseous propellants can be compressed into aerosol dispensers (regardless of the content) before the pressure exceeds 180 psi-gage at 130.degree. F., the limit imposed by the U.S. Department of Transportation for interstate shipping purposes. For example, by injecting nitrogen gas into the largest aerosol can (48.6 in.sup.3 capacity) until the pressure comes to 140 psi-gage at ambient, which is very close to the pressure limit for this container, and then connecting this can to a relatively large P215/85 R15 tire (2454 in.sup.3 capacity if not flattened), the tire pressure can be raised from 0 psi-gage to 2.7 psi-gage. Even assuming no gas loss through the puncture in such a deflated tire, it is seen that many cans of nitrogen gas would be required to attain reasonable tire pressure.
It is a feature of our invention that nitrogen gas (or compressed air) be used in conjunction with dimethyl ether and trichioroethylene to produce the desired vapor pressures over an extremely wide temperature range, extending from below 0.degree. F. to above 165.degree. F. The nitrogen also greatly augments the pressure of the dimethyl ether and trichloroethylene and, thus, facilitates a much faster transfer of the product from the dispenser, since virtually no back-pressure of nitrogen can accrue in the tire to retard the flow rate.
It is a further object of the present invention to create a composite propellant that will exhibit the minimum degree of intrinsic flammability, given the limitations described above. Burning is an oxidative process. For example, when hydrocarbons are burned, totally unoxidized substances are reacted with oxygen to ultimately produce water vapor, carbon dioxide and a large amount of heat. In contrast, the dimethyl ether molecules (CH.sub.3 --O--CH.sub.3) may be considered as partly oxidized hydrocarbon material. About 35% by weight is comprised of oxygen. The remainder is potentially flammable. By calorimetry, it can be shown that the combustion of dimethyl ether only produces about 65% as much heat per unit weight as do the typical hydrocarbon gases; e.g., propane and butane. The presence of non-flammable nitrogen and trichloroethylene acts to dilute the dimethyl ether vapors somewhat, absorbing some of the heat generated if combustion should occur, and raising the Lower Explosive Limit (LEL) to values at least twice as high as those of the commonly used hydrocarbon blends for tire sealing and inflating aerosols.
Because approximately 40% of the weight of the aerosol vapors in the inflated tire is now composed of chemically bound oxygen, trichloroethylene and nitrogen, the combustion of this mixture will produce the heat that is mitigated by the need to also heat up these non-combustible atoms and molecules. Thus, intensely high heating, which may be destructive to tires, can be more readily avoided with our preferred blends of inflating gases.
A final attribute of the inflative process involves the very significant pressure depressant effect exerted upon the dimethyl ether by the other components of the formula. Pure dimethyl ether has a vapor pressure of about 62.5 psi-gage at 70.degree. F. In contrast, the partial pressure of dimethyl ether in the preferred formulations is only 10 to 13 psi-gage at 70.degree. F. This permits more non-flammable nitrogen (or compressed air, or trifluoromethane) to be added and this, in turn, allows the compositions to be used over a substantially wider temperature range than other products of this type.
In the case of aerosol products designed to be stored in cars until needed, such as sealers and inflators, one must recognize that car interiors may be heated to rather extreme temperatures when the vehicle stands for a time in the sunlight during a very hot day. Dark colored cars are especially affected. A study by the Armor All Corporation (Motor Trend Car Care Guide), APR-1993), showed that temperatures ranged from 157.degree. to 241.degree. F. under such conditions. The hottest areas were the dashboard, front seat surfaces and rear deck.
The lag effect in heating up a typical 12 oz. to 20 oz. aerosol can to such temperatures, with only the transfer effects of hot air, is undoubtedly a factor in preventing all but a few car care and service aerosols from becoming so overheated that they eventually buckle and burst. The overheating problem is countered by using formulas with low pressure propellants, with propellants that rise only slowly in pressure when heated, or by using containers that have pressure relief fitments--causing them to leak product if excessively heated. The use of nitrogen, coupled with a higher pressure liquid propellant whose pressure is suppressed by other ingredients, is a useful approach. It provides acceptable pressures from below 0.degree. F. to above 165.degree. F. By reducing the nitrogen content, even higher temperatures can be safely tolerated.
At the same time, the unit may be required to function in very cold conditions. Surprisingly, it has been found that dimethyl ether serves as an excellent anti-freezant for the water in the formulation. The propylene glycol reinforces this effect, keeping the water liquid at least to -20.degree. F.
As is well known to formulators, the freezing of water is accompanied by about a 10% expansion of product volume, and this may permanently distort some full aerosol dispensers. Also, resins, latexes and other polymeric emulsions may evince freeze/thaw instability by breaking down and causing the product to be inverted, agglomerated, or otherwise rendered unfit for use. Perhaps, most importantly, if a motorist requires the product in extremely cold weather conditions, and it fails to work because it has frozen in the can, the result may range from exasperating to life-threatening.
The usual sealant/inflator composition contains about 70% to 75% of water and 4% to 6% of either ethylene glycol or propylene glycol anti-freezes. Solutions of this type freeze at 27.degree. F. to 29.degree. F. From this, it is apparent that the standard compositions are woefully inadequate when one attempts to use them at temperatures of 25.degree. F. or below.
Exacerbating this problem is the fact that a number of sealant/inflator compositions develop such low pressures that they cannot transfer material into the deflated tire if the aerosol is below about 30.degree. to 40.degree. F. This occurs because they include butanes or other low pressure propellants, which provide reduced possibilities for can eversion or bursting if overheated in hot summer weather.